The present invention relates to a method for reducing the heat loss in a heated workpiece, when the workpiece is moved from a furnace to a processing tool, the workpiece being removed from the furnace and displaced on a carrier device to the processing tool, in which it is inserted.
The present invention also relates to an apparatus for reducing the heat loss in a workpiece, when the workpiece is displaced by means of a carrier device from a furnace to a processing tool.
Press hardening is a technique which has become increasingly common, for example as regards the manufacture of car body parts in the automotive industry. Press hardening entails that a workpiece is placed in a furnace, where the workpiece is heated to the intended temperature, often of the order of magnitude of 900° C. or more. As regards car body parts, the workpiece is often a sheet metal piece of a thickness of the order of magnitude of between 0.6 and 2.0 min. When the workpiece has reached the intended temperature, it is removed from the furnace and placed in a press tool where pressing to the intended configuration is carried out. In that the tool is cooled and in that there is extremely good contact between the workpiece and the processing surfaces of the tool, a very rapid temperature reduction takes place of the workpiece so that this is hardened simultaneously with the forming operation.
On inserting the workpiece in the furnace, use is made of a carrier on which the workpiece rests. This carrier May either be permitted to remain in the furnace during the heating time, or alternatively be removed immediately after insertion of the workpiece. In the latter case, the carrier is placed in the furnace again after completed heating and lifts out the workpiece and transfers it to a processing tool.
In the above-mentioned technology, it is vital that the workpiece is at the intended temperature when it arrives in the processing tool. Heat losses during the displacement from the furnace to the processing tool may be considerable in that a workpiece produced from sheet metal has a large surface area in relation to the mass which is heated. At those temperature levels which are under consideration, a considerable proportion of the heat losses is caused by radiation. Nevertheless, the temperature loss may also be influenced by the ambient temperature, variations in the displacement time, draughts and similar factors. In order for the end result to be of the requisite standard, it is necessary that the temperature of the workpiece when it is placed in the processing tool can be kept at the correct level and within narrow tolerances. However, the vital point is that the workpiece does not cool more than from about 930° C. down to approx. 800° C.
It is desirable to design the method intimated by way of introduction such that the heat loss during displacement of the workpiece from the furnace to the processing tool is kept to a minimum and as far as possible without influence from the ambient surroundings.
Concerning the apparatus, an aspect of the present invention resolves corresponding or analogous problems and in addition and an aspect realizes an apparatus which is simple and economical in manufacture and economical in operation.
According to a method aspect of the present invention, a carrier device and workpiece are brought to a position substantially internally in an enclosure with a beat reflecting interior, that the enclosure and the carrier device with the workpiece are moved to the processing tool where the carder device is exposed and the workpiece is passed into the processing tool.
An apparatus aspect of the present invention includes an enclosure with a heat reflecting interior, the carrier device and the workpiece being moveable to and from a position substantially internally in the enclosure, and the enclosure together with the carrier device is moveable from the furnace to the processing tool.